Creating and Characterizing Individual Molecular Bonds with a Scanning Tunneling Microscope

In high school chemistry experiments, it's easy to follow a chemical reaction: Mix the chemicals in a test tube, and watch for a change of color, fizzing, or some other sign of chemical transformation. But what do you do if you want to probe the spatial limits of chemistry—that is, to initiate and examine an individual chemical reaction? In a recent paper in Science, Wilson Ho of Cornell University and his graduate student Hyojune Lee provide an answer. By using a scanning tunneling microscope (STM), Ho and Lee combined atoms and molecules on a metal surface to make new molecules. But that's not all they accomplished. To confirm the chemical identity of their molecular creations, they measured the individual molecules' vibrational energies—again with the STM. “Their results are truly remarkable,” comments the University of Maryland's Ellen Williams, “not just creating the bonding, but also the single‐molecule spectroscopy.”